Many portable electronic devices known in the arts, such as portable computers, use chargers to replenish batteries when access to AC power is available. A common approach requires the use of an AC adapter, which converts the AC power to a fixed output DC voltage, and a charger function that is implemented in the end equipment. Generally, the approach commonly used in the arts requires a system where the charger function has a control function and a power conversion stage. The power stage down-converts the fixed AC adapter output DC voltage by means of either a linear stage or a switching mode converter. The control functions and the charger stage implement the battery charger function that executes the battery charging process.
The control functions monitor specific battery and system parameters such as (but not limited to) battery voltage and/or battery current, compares each of them to a reference value, and generates an error signal as needed, that is sent to the charger power stage. This error signal, in turn, adjusts the power stage duty cycle (in DC/DC conversion power stages) or the power stage pass element conductance (in linear power stages) in order to set the battery charge current or battery charge voltage to the desired value. Control functions that monitor distinct pack or system parameters other than the battery charge current or battery charge voltage may be added to the system, depending on the overall system requirements.
The approach for the interface between the control function and power stage generally known in the arts requires the inclusion of both the control function and the power stage in the end equipment, with the AC adapter output voltage being of a fixed value. As a result, in this approach the AC adapter output voltage is not dependent on the error signal generated by the control function. This approach results in many disadvantages in commonly used battery charger control topologies, including but not limited to the high cost of power stage elements such as inductors, filter capacitors and MOSFET switches in DC/DC power stage topologies, and linear pass elements (usually MOSFET switches) in linear power stage topologies. System efficiency suffers as a result of the conduction and/or switching losses in the power stage. Power dissipation in the end equipment is increased by converter stage power dissipation.